Polyester fiberfill (sometimes referred to as polyester fiberfilling material) has become well accepted as a reasonably inexpensive filling and/or insulating material for pillows, cushions and other furnishing materials, including bedding materials, and in apparel, because of its bulk, filling power, aesthetic qualities and various advantages over other filling materials, so is now manufactured and used in large quantities commercially. Crimp is a very important characteristic. Crimp provides the bulk that is an essential requirement for fiberfill. Slickeners, referred to in the art and hereinafter, are preferably applied to improve aesthetics. As with any product, it is preferred that the desirable properties not deteriorate during prolonged use; this is referred to generally as durability. In the case of fiberfill, a very desirable property is the ability to recover from compression, so as to provide the desired aesthetics after repeated and/or prolonged compressions, and provide the desired degree of softness (or firmness) again and again when recompressed. Although this has been desirable, little has been published on fiberfill properties that provide durability.
Originally, as with other polyester fibers, solid fibers of round cross-section were used, being the least expensive fibers to make, and such solid round polyester fiberfill is still used commercially. Some twenty years ago, however, hollow polyester fiberfill was suggested and used, as disclosed, e.g., by Tolliver in U.S. Pat. No. 3,772,137 and by Glanzstoff in GB Patent No. 1,168,759. Tolliver shows a single hollow core, i.e., a central continuous longitudinal void. The preferred shape of the void was non-round in cross-section, but voids approximately circular in cross-section were also disclosed, and large quantities of hollow polyester fiberfill having single central voids of circular and of non-round cross-section have been manufactured and used because of their greater lightness (lower density), in contrast to solid fiberfill, and because of the improvement in insulating power, and for other aesthetic reasons. More recently, there has been provided an improved hollow polyester fiberfill, characterized by four equisized, equispaced, non-round voids around a solid axial core, the filament cross-section having a quadrilateral peripheral contour defined by four flattened sides and four rounded corners, in conjunction with a saw-toothed type of crimp configuration and a slickening agent, to provide high bulk and high bulk durability with improved softness more like that of natural down filling, as disclosed in EPA2 67,684. Thus, this 4-hole cross-section has been believed superior in various respects, including bulk durability.
In the course of my considerations of how to make further improvements in fiberfill, and of my analysis of existing forms of fiberfill, I considered the possibility that important advantages could perhaps be obtained by making further changes in the cross-sectional shape of hollow filaments. However, as is well known, it is difficult to melt-spin filaments with multiple voids (especially from polyester) so it became necessary for me to design an entirely new spinneret, with new orifices, in order to spin hollow filaments according to the present invention. This new spinneret is the subject of my application, Ser. No. 07/225,807, now U.S. Pat. No. 4,836,763.